Nowadays, various electronic components operated at a high frequency are mounted on an electronic apparatus such as a personal computer or a personal digital assistance. Then, in such a type of electronic apparatus, a wiring substrate with a capacitor built-in type has been proposed in order to effectively absorb high frequency noise.
For example, FIG. 11 of Japanese Patent Application Laid-Open No. 2008-78301 (“Patent Literature 1”) proposes a wiring substrate with a built-in capacitor equipped with an aluminum sheet 101 (sheet base material) that is positioned inside the wiring substrate and in which at least one of surfaces thereof is a metal, a dielectric layer 102 positioned on the metal surface of the aluminum sheet 101, and a solid electrolytic capacitor 105 (flat surface type capacitor) composed of a conductive polymer layer 103 and a capacitor electrode layer 104 and positioned on the dielectric layer 102, and equipped with a first conductor 106 that is insulated from the capacitor electrode layer 104 and that reaches the metal surface of the aluminum sheet 101 from a surface of the wiring substrate, a pad 107 for power source (first electrode pad) connected to the first conductor 106 and positioned on the surface of the wiring substrate, a second conductor 108 passing through the aluminum sheet 101 and insulated from the aluminum sheet 101, and a pad 109 for ground (second electrode pad) connected to the second conductor 108 and the capacitor electrode layer 104.
In Patent Literature 1, the foil shaped aluminum sheet 101 is subjected to electrolytic etching in hydrochloric acid aqueous solution to make the surface of the aluminum sheet 101 be roughened, and thereafter the surface is anodized in aqueous solution of ammonium adipate and an oxide film is formed on the surface of the aluminum sheet to thereby form the dielectric layer 102.
This structure provides a low cost wiring substrate with a built-in capacitor that exhibits a large capacity.
However, since the capacitor is formed by the solid electrolytic capacitor 105 having the dielectric layer 102 anodized, although the dielectric layer 102 of a thin film can be obtained, the capacitor has many defects such as insufficient in insulation properties and inferior in reliability. Furthermore, since the dielectric layer 102 is formed by anodization, polar character is applied to the capacitor, resulting in deterioration in usability.
The present invention has been conceived in light of such a circumstance, and an object thereof is to provide a thin film capacitor small in size and large in capacity that is good in usability and large in degree of freedom in design and that can be applied to various use applications, and to provide an electronic apparatus including the thin film capacitor.